1. Field of the Invention
The present invention concerns a fluid clutch for transmitting a driving torque of a driving disk to a casing by an oil supplied to a torque transmission chamber and, more in particular, it relates to a fluid clutch for controlling the rotation of a cooling fan for an automobile engine attached to the casing.
2. Description of the Prior Arts
A known liquid clutch has a structure, for example, that the inside of a casing is divided by a partition plate into a torque transmission chamber and an oil reservoir, a driving desk rotatably is contained in the torque transmission chamber and disposed such that it is driven rotationally by a driving section, an oil in the oil reservoir is supplied from a supply control aperture formed to the partition plate to the torque transmission chamber, and the oil in the torque transmission chamber is returned by way of a dam disposed to the inner circumferential surface of the tightly sealed casing opposed to the outer circumferential surface of the driving disk and a discharge channel in communication with the dam to the oil reservoir chamber thereby controlling the amount of the oil in a torque transmission gap between the driving disk and the inner wall of the torque transmission chamber.
In the liquid clutch of the aforementioned type, a driving torque of the driving disk is transmitted to the casing by the oil supplied from the oil reservoir to the torque transmission chamber, and the fan attached to the casing is rotated to cool, for example, an automobile engine. As the oil, a silicon oil having a high viscosity is used generally for attaining the torque transmission function.
However, the fluid clutch of the prior art involves the following problems.
That is, when an engine is restarred in a state where a great amount of the oil is present in the torque transmission chamber or upon quick acceleration during running, abrupt the rotation speed of is caused, the casing on the driven side (cooling fan) is also increased quickly although only for a while by the oil in the torque transmission chamber accompanying the acceleration of the driving disk on the driving side. The phenomenon is generally referred to as "co-rotating" phenomenon which has to be prevented since this causes fan noises or unpleasant feeling caused thereby and also increases a fuel cost.
The "co-rotating" phenomenon in the fluid clutch of the prior art upon restarting of the engine occurs more remarkable as the amount of the oil in the torque transmission chamber is increased. As means for overcoming the problem, it has been proposed, for example, in Japanese Patent Publication Sho. 63-21048 to introduce the oil flowing out of the discharge control aperture of the partition plate once in a diametrically opposite side and then supplied into the torque transmission chamber.
In such a structure, when the engine stops in a state where the oil is scarcely present in the torque transmission chamber and a great amount of oil is present in the oil reservoir, since the oil does not flow from the oil reservoir to the torque transmission chamber, the "co-rotating" phenomenon does not occur upon restarting of the engine. However, this structure has no effect for preventing the "co-rotating" phenomenon upon restarting of the engine when it stopped in such a situation that a great amount of oil is present in the torque transmission chamber or upon quick acceleration during running.